1. Field of the Invention
The present invention relates to an ion implantation apparatus. More particularly, the present invention relates to an ion implantation apparatus for scanning a wafer with an ion beam to implant ions into the surface of the wafer in the fabricating of a semiconductor device.
2. Description of the Related Art
In general, an ion implantation process is one of the processes used to fabricate a semiconductor device. In this process, particles of a predetermined impurity are accelerated and are formed into an ion beam directed towards a particular part of a wafer. The ion beam or the wafer is continually moved horizontally or vertically, whereby the ions are implanted into the entire surface of the wafer.
A conventional ion implantation apparatus is disclosed in Japanese Patent No. Hei 04-283923. The apparatus, as shown in FIG. 1, comprises: parallel ion beam radiating means 10, a mask 16 having a slit 17 therein, a support plate 12 for supporting a wafer 11, elevation driving means 14 for raising and lowering the support plate 12 via a driving shaft 13 integral with a bottom part of the support plate 12, and an electrostatic flux type of charge monitor 15 disposed near the bottom of the ion beam A as it passes through the slit 17 in the mask 16.
The parallel ion beam radiating means 10 produces an ion beam A. The ion beam A passes through the slit 17 of the mask 16, and is accelerated by a separate speed-up pipe. Then the ions of the beam A are then implanted into the wafer 11 mounted on the support. At this time, the driving shaft 13 is raised and lowered by the elevation driving means 14, while the support plate 12 is tilted horizontally or vertically by about 7 degrees, to execute a scanning process in the Y-direction.
Moreover, at this time, the topmost and bottommost parts of the wafer 11 are offset horizontally from each other by a distance X due to the slope of the support plate 12. That is, there is a difference in the distance that the ion beam A propagates from the parallel ion beam radiating means 10 before reaching the topmost and bottommost parts of the wafer 11. This difference brings about a variation in the amount of ions distributed over and hence, implanted into the wafer 11. These variations in the amount of ions implanted into the wafer 11 create a variety of problems, such as inconsistencies in the quality of the semiconductor devices produced from the wafer. Some of the devices are even of insufficient quality.
Therefore, one object of the present invention is to solve the aforementioned problems by providing an ion implantation apparatus that minimizes the difference in distance that an ion beam must travel before reaching topmost and bottommost parts of a wafer during the scanning of the wafer, whereby the ion-implantation process is carried out uniformly across the surface of the wafer.
Another object of the present invention is to provide an ion implantation apparatus which can achieve such a uniform distribution of ions for wafers of various sizes and produce different characteristics in the wafers as the result of the ion-implantation process.
In order to achieve the aforementioned objects, the present invention provides a wafer scanning support which includes a scan shaft pivotally mounted about a horizontal axis so that it can be inclined relative to the vertical, an elevating member slidingly coupled to said scan shaft so as to be movable therealong, a driving motor for moving the elevating member up and down along the scan shaft, and a wafer holder connected to the elevating member so as to be movable therewith.
The wafer scanning support unit may also include horizontal maintaining means for positioning the wafer holder in the horizontal direction. The horizontal maintaining means includes a horizontal transfer member coupled to the elevating member so as to move therewith. On the other hand, a vertical maintaining means is provided for positioning the wafer holder in the vertical direction. The vertical maintaining means includes a vertical transfer member coupled with an end of the horizontal transfer member so as to move therewith.
The wafer holder can be incorporated into a tilter mounted to an end of the vertical transfer member. The tilter is operative to place the wafer holder in an upwardly facing position to facilitate the loading or unloading of the wafer.
According to the present invention, the scan shaft can be inclined at a predetermined position. As the elevating member is moved upwardly and downwardly along the scan shaft during scanning, the inclined wafer holder is moved along an inclined path corresponding to the inclination of the scan shaft, whereby the ion beam travels substantially the same distance to impinge all portions of the wafer including the uppermost and bottommost parts. In addition, the position of the scan shaft can be set based on the parameters of the process, such as the size of the wafer and the desired characteristics to be provided by the ion-implantation process.
Moreover, the horizontal and vertical maintaining means allow the wafer support to be moved to the same loading and unloading position irrespective of the position of the scan shaft.